If you're thinking about buying a used car, then you're probably concerned about reliability. After all, used cars have been driven before, meaning they don't come with the same peace of mind as a brand-new model with a long warranty. They also don't have the same brand-new components, which means they could experience some costly problems.

Of course, one of the biggest and most expensive parts of any new or used car is the transmission, so we've outlined some easy ways to tell if the car you're considering is having problems with its automatic transmission. By following these tips, you can safely pass on a faulty car, rather than drive it home and face a costly repair.

Slipping Gears

One of the major signs that an automatic transmission is starting to fail is if the transmission begins slipping gears. While this can be easy to diagnose in a car with a manual transmission, it's a little harder when the car is an automatic, especially if it's in the early stages of failure.

Still, the main symptom for a car that's slipping gears is simple: If the engine is making noise and the tachometer is climbing without the car accelerating, it's likely that the transmission is slipping. To check whether this problem is affecting you, we suggest keeping an eye on the tachometer or listening to a car's engine while you're on a test drive. Next, push the accelerator. If you notice that the tachometer is climbing but the car isn't increasing in speed, the car is probably suffering from the early stages of transmission trouble.

Rough Shifts

Another common problem among cars with transmission trouble is rough shifting. This one is a lot easier to diagnose than slipping gears because you can check it while the car is sitting still. Simply shift the car from park to reverse, or from park to drive, and observe what happens. If there's a big clunk or the car seems like it's lurching, this could be an early sign of transmission trouble.

To verify that the rough shifting is indeed a problem with the car's transmission, put the car into drive and spend some time with it on the road. If the car's shifting is smooth and drama-free when you're cruising at normal traffic speeds, the clunk noises that occur when going into reverse or drive may be another issue. But if the clunking is also taking place while the car shifts gears as you drive down the street, then you've got transmission problems.

Delayed Gear Engagement

Another major sign of trouble comes if an automatic transmission experiences a delay before switching into gear. For example, if you shift from P to R or from P to D and the car doesn't do anything for a few seconds, it's likely that there's a serious problem with the transmission. The gear lever shouldn't act as a suggestion for the car to go into gear but rather a mandate, so if the transmission doesn't immediately enter your desired gear, something probably isn't right.

Fluid Leaks

If you experience any of the problems listed above when going through the process of buying a used car, then we strongly suggest that you check the car's transmission fluid or bring it to a qualified mechanic who can do it for you. Low or empty automatic transmission fluid could cause a complete breakdown of a car's transmission, and any car experiencing the above symptoms may be suffering from that exact problem. A car's transmission fluid should be red in color and should smell sweet. If the fluid has turned black or it gives off a burning smell, there could be a serious problem with the transmission. Alternatively, the fluid may just need to be changed, and we suggest trying to change it before you pass on the car entirely.

author photo

Doug DeMuro has a wide range of automotive industry experience, from work at a Ferrari dealership to a manager for Porsche North America. A lifelong car enthusiast, Doug's eclectic vehicle purchases include a Porsche 911 Turbo, an E63 AMG wagon, an old Range Rover and a Mercedes Benz G-wagen.

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